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  1. #1

    Some thoughts on pond heating methods....

    Some thoughts on heating your pond......

    The total running costs of various heaters are not always that simple to work out.
    I have used this reasoning when working out heating for other projects.

    For most of us, electricity is approximately 4X the cost of mains gas per kWh.

    In an electric inline heater, 100% of every kW makes heat, so let's say that costs 15p per kWh.
    As a standalone system, this is the easiest to install (other than drop in heaters).

    A gas boiler and heat exchanger system may be 85% efficient (boiler itself is higher than that), so in comparison that would cost 4.3p per kWh (corrected for efficiency rating)..
    This can be a cheap install if you can make use of your existing gas boiler system, but expensive if you need a dedicated boiler and gas supply.

    How about an airsource heat pump?
    I will assume you heat the water to between 15-20 degrees (heat pump COP is very much affected by water temp required).
    The efficiency of the heatpump will vary a lot depending on air tempreature and if it's cold, air humidity.
    If the air is at 0C, a decent heat pump will have a COP of about 4 to heat to 15/20C. This suggests a cost of 3.75p per kWh.
    A good (and there are some not so good ones so beware) ASHP install will cost a similar amount to a new gas install for a low heat output unit suitable for a pond application.

    ASHP notes:
    If the air is cold and humid the condenser on an ASHP can freeze and the unit will need to defrost. This will increase running costs significantly during the defrost cycle.
    As air temperatures rise the COP will rise and the cost per kWh can come down to about 3p per kWh. Of course as the weather warms up less heat is required and the very highest COP values of an ASHP aren't really relevant.

    The above is based on my own experience, but there will be proper experts out there who will be able to give more accurate info.
    I hope it has been of some use.


    Last edited by Ukzero; 09-12-2020 at 01:17 PM.
    My DIY ponds from 1988 until present day.
    All can be found here:
    https://www.ukzero.com/pond.htm

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  3. #2
    Extreme Koi Member Rank = Grand Champion Andre Asagi's Avatar
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    Ease of install is significant. Anyone can install an online electric heater. Most people could install an ASHP with a small amount of reading or (in my case) a few diagrams from Manky Sanke.

    However I have yet to encounter anyone who can explain practically how to install a heat exchanger from an existing boiler.

  4. #3
    Quote Originally Posted by Andre Asagi View Post
    However I have yet to encounter anyone who can explain practically how to install a heat exchanger from an existing boiler.
    In practice the main parts are a 3 port motorised valve to control a separate heat exchanger loop, pipework, a suitable heat exchanger (Bowman for example) and a control box.
    The control box would have inputs from a thermostat in your pond, the 3 port valve, boiler and probably your house thermostat for priority setting.
    I would use these inputs and some simple c/o relays to operate the system as follows:
    Domestic hot water priority (automatic in a combi boiler).
    Switchable heating priority, home first, pond first, shared.
    Now this would be a DIY control box - I don't know if you can buy such things ready made.

    If you have installed or modified your home heating and understand basic circuits (need not use electronics) none of this should be a major problem because you leave the boiler well alone.
    Obviously if you have no experience here it can look quite daunting and will definitely influence your choice.

    I am considering making just such a system to heat our hot tub. If so the wiring schematics and components will be identical (apart from using a Ti heat exchanger to cope with Cl in hot tub).
    If I proceed I might spend the time to produce a guide if there is sufficient interest.
    Last edited by Ukzero; 09-12-2020 at 01:42 PM.
    My DIY ponds from 1988 until present day.
    All can be found here:
    https://www.ukzero.com/pond.htm

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  6. #4
    Extreme Koi Member Rank = Supreme Champion john1's Avatar
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    I am sure quite a few on here would be interested myself included but in simple language.
    John

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  8. #5
    Senior Member Rank = Nanasai GadgetBazza's Avatar
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    Hi UKZero,

    I did something very similar on the swimming pool and pond at my last house.

    So I had a dedicated gas boiler for the swimming pool, no DWH, just a heat exchanger on a very short circuit. I had a crude heat control setup using a thermostat on the return line, but since the heat exchanger heating circuit runs at much higher temps that then pool water flowing through it, the control was almost useless. So I created a circuit to manage this using a digital thermostat controller which worked much better.

    For the pond, which was located next to the house, my filter room was right outside the kitchen, so I tee'd into the heating circuit where the boiler was in the garage with electronic control valves (not 3 port in this case, so I didn't have control between pond and house, but basically heated the pond only when the house was heating - we tend to have the heating on permanently at a lower setting). I ran some new pipes from the control valves in the garage which was conveniently located behind the kitchen, under the kick boards and out the back wall into a heat exchanger.

    I then used another of the digital programmable thermostats to call for heat by way of opening the control valves. The idea was not to "add" to the heating cost of the house, but make use of the heating when it was running if the pond needed it. Thinking about it now, it might create some variation in heat based on how your house heating is operating, but I never experienced any issues in this manner. In any case, it can be designed out by using three port valves as you suggested.

    I'll try and find the digital programmable thermostats I used, or something similar, they actually seem very similar to the front panel you get on an Elecro device.

    I guess there will be some issues with guiding people on doing this, creating circuits with mains relays can obviously be very dangerous... I know, I blew the back clean off a plug when I plug my circuit in first time because I had the relay base upside when I was feeding the wires into it and wired it in a complete mirror to how I should have done!!! Tend to check things over a few times now before "playing" these days!

    I've recently put a control circuit around my pool pump and air source heat pump, so that I can run it manually on or off, or in an auto position where the pump can be triggered either by the ASHP indicating it wants to heat the pool water, or running the pumps via a schedule or from my house automation system. I will possibly be doing some more to this in the future as I am using the ASHP to run the pond in the cold months and at the moment, I have a circulation pump and the ASHP on manual control only at the moment.

    Going back to your original point though, I think if you have the potential to connect into the heating circuit on the house, the heat exchanger option works pretty well. For those not fortunate enough to be able to run pipework from near the boiler flow and return circuits because of logistics, if your pond is still close to the house but not near the boiler, you can still consider tee'ing into the flow and return of the heating circuit, but you will only be able to heat the pond at the same time as the radiator heating is on - which as I said is how I ran mine, so still potentially an option.

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  10. #6
    Interesting reading GadgetBazza
    I built my own swimming pool at our last house (https://www.ukzero.com/garden.htm) and also built a small boiler circuit as you mentioned. I then got a certified heat engineer to commission it.
    We had no gas in the village so the choices were ASHP and oil boiler or bottled gas.
    Budget and running costs were important (the whole garden and pool cost about ?15k) so I put a lot of thought into which way to go and the result surprised some. We were fair weather swimmers. If it was a nice weekend we would use the pool.
    At the time ASHP (unless you bought an industrial one) were putting out an average of 6-8kW. A no frills oil boiler could put out up to 40kW.
    We would either need to keep the pool up to temp all the time ready for use using the ASHP or, as we did, look at the forecast, if it's good, put the oil boiler on overnight at 40kW have a warm pool.
    It just shows that when planning heating there can be a lot of variables to consider and there is no one size fits all.

    For pond heating with domestic heating it would be possible with standard 3 port valves, some relays and something like an STC1000 stat (I use one to heat my pond as here:https://www.koiforum.uk/koi-carp-cha...-solution.html) to design a system which allows you to prioritise between house/pond as suits with a high level of control.
    If I do post something more specific, it would be as a circuit diagram and schematic only. Those who understood it could make their own judgements and those who are less experienced could choose to seek professional assistance.
    I would not produce a detailed "how to" aimed at general DIY hobbyists. Not because I don't want to be helpful, but because I don't want to become responsible in anyway for potential accidents.

    In practice, the control part of such a system should be something most domestic heating engineers should be able to do as it is to all intents and purposes just another zone in a zoned system layout.
    Last edited by Ukzero; 17-12-2020 at 11:56 AM.
    My DIY ponds from 1988 until present day.
    All can be found here:
    https://www.ukzero.com/pond.htm

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  12. #7
    Senior Member Rank = Adult Champion Mikeh83's Avatar
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    I think this shows it quite simple

    You basically would need 2 motorised valves to split the zones and a thermostat for each.

    Below is an example of a combi boiler


    Just imagine one of the zones being the heat exchanger

    The valves cost around ?40 and then you would just have a mechanical pressure bypass valve so if the boiler needs to run when the valves are both shut it can.

    This would be the wiring


    Nothing overly complex in it.


    Sent from my iPhone using Tapatalk

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  14. #8
    Senior Member Rank = Adult Champion Mikeh83's Avatar
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    To add to the above you could also add more zones to say split upstairs and downstairs.


    Sent from my iPhone using Tapatalk

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